10 YEARS FOLLOW-UP RESULTS OF MULLER SELF-LOCKING CEMENTED TOTAL HIP-PROSTHESIS

Purpose of the study This study concerns the analysis 10 years follow-up survival, of the Muller self-locking cemented straight stem, inserted with a cemented polyethylene socket. Material 193 Muller self-locking cemented straight stems were inserted by the author between january 82 and March 83. The first part of the study is a survival analysis of the individual components. The second part is a clinical and a radiological evaluation of 93 hips reviewed at 10 to 11 years with the initial components. Results Using revision of the components as the definition of failure, survival analysis depicted 94.3 per cent survival for the socket (86.5 per cent), and 98.3 per cent for the femur (95 per cent). 7 sockets and 2 stems were revised in 7 patients (one of them is a late infection at 9 years). Up to date this revisions have been successful. 93 patients, 50 females et 43 males, were reviewed, at an average follow-up time of 10.5 years, with the initial components. 70 hips were rated excellent, 12 good, 9 fair and 2 poor. The two poor results presented stiff joints at follow-up. Complete radiographic studies were available for these 93 patients. 38 sockets had no bone-cement radio lucent lines, 52 had limited non progressive radiolucent lines, 3 had a circonferential radiolucent zone aroud the cup two of them migrated. The mean polyethylene wear was 1.30 mm (0.4-2.6). On the femur, there was a low incidence of radiolucencies : 9 patients had limited radiolucencies on the AP view, 4 on the lateral view, with no stem settling more than 3 mm. Demarcations occured predominantly in Gruen zones 5 et 6 with undersized stems placed in valgus. 13 per cent of the femurs presented some degrees of osteolysis with internal defects of the medial cortex, one was extensive. Discussion The clinical result of the stem was satisfactory but roentgenographic evaluation revealed signs of osteolysis in 13 per cent of the femurs. This mecanism of bone loss has been clearly documented to occur because of accumulated polyethylene wear debris, a factor wich also accounts for the high failure rate of the socket. It could be related to the high friction produced by the 32 mm metallic head. Migration of the debris along the medial cortex is probably consecutive to the design of the self locking stem with a lack of cement on the borders. Conclusion The satisfactory long-term results of the cemented straight Muller stem encourage us to continue, but the 32 mm metallic head should be abandonned. We prefer the use of a 32 mm alumina ceramic femoral head combined with the same stem and polyethylene acetabular cup. The study of this next serie with the same follow-up is currently being evaluated.